PMO issues

[JOE911]

Hi Guys,

First time on the forum so please be gentle with me! I have a 1974 911s, I have always wanted to replace my CIS K-jet on my 2.7 with PMO carbs but I was talked around to going with PMO EFI with Heltech 750 ECU. I am sure that there are others out there in "Porscheland" who may have the same or similar setup. I have had nothing but issues trying to have it tuned correctly! the car has been back to the Dyno shop at least 5 times over a 4 month period and it is still not right! The Dyno guy keeps telling me that the 40mm throttle bodies are too big for the motor and that is what is coursing the issues. First attempt at tuning the car it came back with great top end and drivability.... as long as you drove it like a race car which was a lot of fun! But the car was brutal to drive at normal speeds and in stop/start traffic! The real issue in stop/start traffic is that every time you shift gears and released the clutch the car would fire back to life and give you a very violent kick in the back! To try to help you understand it a little more I will try to break it down. While on the down shift... or up shift for that matter, depress the clutch down shift or up shift and then release the clutch as applying the throttle, and this is where the issue starts, while trying the apply the throttle, you are met with resistance from the throttle peddle until you apply enough pressure to break through the pressure point, then you are greeted with a massive thump in the back as the motor fires up again! Also when you back off suddenly the motor will produce a very loud backfire which is great when you want to scare all the lovely Grannies in the street! The car was at the Dyno guy again recently for just over 2 weeks, he called me to say that there was nothing else her can do to improve the setup and I was told "It is what it is"! and if I could pick up the car asap as he needed the get my car out to make room in the workshop (he was very nice again it)! That night I was updating my son about the conversation I that with the Dyno guy, so my son did some searching on line and found a "Tread" on "Sticky Throttle Bodies", I forwarded this onto the Dyno guy who replied they "I'll give it a go but no promises". The next day we picked up the car and low and behold, although not at 100%, the car is 90% drivable in Stop/start traffic, its not perfect but manageable, the throttle peddle has a lot less resistance but the resistance is still there and the poor motor is still backfiring loudly regardless if you are up or down shifting! 

I have spoken to PMO directly and they stand by their recommendation for the 40mm for the 1974 2.7 motor. All the research I had done always came back to the 40mm being the correct option, even Porsche recommend PMO to replace the old Webbers as they are no longer being made!     

Sorry for the long post, but I am really desperate to get the car running correctly so I can enjoy it and I am hoping by joining this forum I'll finally be guided in the right direction!

I've also attached a photo so you can see the final setup. Any help and input will be very much appreciated.

[Lucky Phil]

Welcome to the forum.  Engine compartment looks nice.   I am certain that you have come to the right place.  We have some really smart people on the Forum who will certainly be able to help you.  I will be interested to read suggestions and hopefully see your problem solved.  

[Cheshire Cat]

Does she idle ok? Any chance to see the ign map and air\fuel?

[Raven]

Also are all of the throttle linkages  functioning correctly nothing binding or catching on anything and installed correctly ...........??

[JOE911]

1 hour ago, Lucky Phil said:

Welcome to the forum.  Engine compartment looks nice.   I am certain that you have come to the right place.  We have some really smart people on the Forum who will certainly be able to help you.  I will be interested to read suggestions and hopefully see your problem solved.  

Thanks Phil,

I’m hoping I’ll get directed in the right direction & thanks for your kind comment about my engine bay

39 minutes ago, Cheshire Cat said:

Does she idle ok? Any chance to see the ign map and air\fuel?

Hi Cheshire Cat,

idle is OK, it idles at 1000 rpm which is a little high but OK, it ides smoothly and starts very well regardless if it’s a hot or cold start. I’ll see if I can extract a copy of the mapping and post it.

27 minutes ago, Raven said:

Also are all of the throttle linkages  functioning correctly nothing binding or catching on anything and installed correctly ...........??

Hi Raven,

all linkages are super, super smooth... that was the first thing that I had checked

[Cheshire Cat]

6 minutes ago, JOE911 said:

all linkages are super, super smooth... that was the first thing that I had checked

all of them? Bell crank (on the gearbox) and In the foot well? 

[Cheshire Cat]

not sure if it will help but 

http://forums.pelicanparts.com/911-engine-rebuilding-forum/801692-pmo-46mm-carburetor-installation-3-2l.html

 

[Merv]

Many fuelling issues are actually electrical.  Are you checking that system?

[Buchanan Automotive]

In relation to the throttle i would disconnect the throttle linkage ball joint in the engine bay, basically disconnecting the PMOs from the rest of the car. Then you can see if the problem is with the car or the PMOs. Im guessing the issue still lies within the PMO setup, either one of the butterflies may be sticking or the throttle return spring is too strong.

Your backfiring issue will come down to tuning, sounds like a little too much fuel entering the engine after closed throttle, or it could be the camshafts you are using/ combination of both. May i suggest a better silenced muffler may help you out here as well. 

Regards

Sean                                                            

[michel]

... is where the issue starts, while trying the apply the throttle, you are met with resistance from the throttle peddle until you apply enough pressure to break through the pressure point,...

it may not be the issue and Sean above met your question with a good response

however if your gearbox bell rank ain’t the right one and, close enough ain’t going to cut it ... you will have noticeable throttle issues . That is requiring considerable pressure and then it ‘relaxes’. 

however that itself, should not cause the fuelling Back firing issues 

if you are still stuck (pun aware) get in contact with me, as I do happen to have as a best mate PMO’s ex production  engineer living  In Canberra 

A few further things 

Richard is always right 

who knows what PMO stands for .

and @JOE911 pretty engine bay

[JOE911]

Guys,

A big thanks to all of you... All your suggestions and thoughts have been explored over the last (guessing) 3 to 4 months. Peddle box checked, throttle cable and linkages checked, PMO linkages and Butterflies checked, wiring and crankshaft sensors  checked, my gut feeling is the ECU mapping and tuning, does anyone know of a good Heltech tuner in Sydney? 

[Raven]

Hamiltons Autohaus or PR Technology  both in Northern suburbs 

[JOE911]

Haha... Hey Raven,

Its funny you suggested "Autohaus Hamilton",  I was a Autohaus Hamilton customer well over 30 years ago when it was still owned and run by Ian & Christine Hamilton when the workshop was still in Dee Why, I still have service receipts in my files from the mid 80's! It was Ian Hamilton who sold the business to the current owner Grant, they are truly a great bunch of guys with a A1 operation! Funnily Autohaus does not have their own Dyno nor Heltech or Motech tuner, they farm this sort of work out as required! I did speak to Grant about my issues and he did suggested a couple of Tuners, but when I spoke to them it was like "Oh another Porsche tragic we can suck dry"! Just got a real bad vibe from them!  

I am not aware of PR Technology, I'll look them up.

[Cheshire Cat]

1 hour ago, JOE911 said:

Guys,

A big thanks to all of you... All your suggestions and thoughts have been explored over the last (guessing) 3 to 4 months. Peddle box checked, throttle cable and linkages checked, PMO linkages and Butterflies checked, wiring and crankshaft sensors  checked, my gut feeling is the ECU mapping and tuning, does anyone know of a good Heltech tuner in Sydney? 

The problem is if it feels like you have to push through something, if you have a resistance at some point - it`s a mechanical problem. Unless you have dbw throttle. If it just feels like it, I mean the pedal is smooth all the time and you have to just add much more fuel - then it`s tuning. 

[clutch-monkey]

On 17/06/2020 at 19:16, Raven said:

Also are all of the throttle linkages  functioning correctly nothing binding or catching on anything and installed correctly ...........??

this happened to me. wasn't immediately obvious but when driving a fuel line moved slightly and the throttle arm would squeeze past it with resistance.

unfortunately the fuel line then blocked it from returning to idle, jamming it at WOT.

was a wild ride

[Mike D'Silva]

On 17/06/2020 at 18:03, JOE911 said:

 greeted with a massive thump in the back as the motor fires up again! Also when you back off suddenly the motor will produce a very loud backfire

 

Does the engine actually die when you change gears and take your foot off the pedal?

Perhaps he has the decel fuel cut set incorrectly. 

When I first got my car back from a tuner, I found that every time I would try to take off from a standstill, it would virtually stall.. Squeezing the accelerator and letting out the clutch simultaneously, would result in a stall, but I managed to alter my fuel settings sufficiently to fix this.

If it is backfiring when you back off the throttle, I'm guessing it must be either very lean or very rich (I'm not smart enough to know which one)... I bet if you posted some of the tables here, someone would be able to help out.

[Cheshire Cat]

18 minutes ago, Mike D'Silva said:

If it is backfiring when you back off the throttle, I'm guessing it must be either very lean or very rich (I'm not smart enough to know which one)...

I`d put money on lean. 

Transitions are pretty nasty to tune I find

[Raven]

10 hours ago, JOE911 said:

Haha... Hey Raven,

Its funny you suggested "Autohaus Hamilton",  I was a Autohaus Hamilton customer well over 30 years ago when it was still owned and run by Ian & Christine Hamilton when the workshop was still in Dee Why, I still have service receipts in my files from the mid 80's! It was Ian Hamilton who sold the business to the current owner Grant, they are truly a great bunch of guys with a A1 operation! Funnily Autohaus does not have their own Dyno nor Heltech or Motech tuner, they farm this sort of work out as required! I did speak to Grant about my issues and he did suggested a couple of Tuners, but when I spoke to them it was like "Oh another Porsche tragic we can suck dry"! Just got a real bad vibe from them!  

I am not aware of PR Technology, I'll look them up.

The are at Brookvale on Northern Beaches 

[P-Kay]

I thought Halltech are in Sydney? Why not go straight there?

[ber914]

Chris @ XSFLOW  - 9972 0100.

Set up my Duratec race engine on a Haltech 1500 -runs great.

Rob

 

[JOE911]

P-Kay,

Yeah Haltech are in Sydney. I spoke to them yesterday and they referred me to another Tuner which I visited  yesterday afternoon, he is confident he can sort it out , so much so, he said that if he cant sort it he will not charge me for his or his Dyno time which was music to my ears! (he'll probably sting me with a huge bill if he sorts it;-) Its booked to go in on the 30th June, I'll keep you all posted, fingers crossed.

[sus911]

The alternative would have stung you, regardless of the outcome!

[JOE911]

Ha, you’re correct with your assumption! Looking forward to the conversation with him if the tune gets sorts!

[Lucky Phil]

Joe, watch a few episodes of mighty car mods.  Marty and Moog are always going to a guy in Sydney to get their cars tuned on Haltech gear.  Or drop them a mail and they will be able to give you his details.  The video below has their guy in it

 

 

[JOE911]

Thanks Phil'

Thanks for the link. Its great to see some Aussie content!